Contact lenses fulfill approximately one-third of all ophthalmic correction needs with over 125 million wearers worldwide. The contact lens industry has made great advancements in the field of vision correction. Manufacturers are progressing toward providing contact lenses that are designed to match a patient's refractive correction and fit. By moving beyond standard spherical lenses, manufacturers will be able to provide contact lens wearers with better visual acuity and overall comfort. For contact lens manufacturers, the size and diversity of the worldwide marketplace leads to a variety of contact lens designs and products providing treatment for myopia, hyperopia, presbyopia, and other conditions related to eyesight.
Many metrology methods rely on techniques used for rigid lenses and are not useful for measuring soft lenses. The very nature of a soft contact lens often precludes the use of these conventional metrology methods. A typical soft contact lenses has a thickness on the order of 100 μm-200 μm. Soft contact lenses can range from approximately 25% to 75% water by volume, are unstable in the air due to evaporation and given the general shape and materials necessary for eye performance, soft contact lenses lack the structure to support kinematic mounting.
Current metrology, such as methods based on focimeters and moiré deflectometry, lacks the combination of spatial resolution, high sensitivity, and large dynamic range desired to accurately measure more advanced lenses. These metrology techniques generally are limited to ophthalmic testing of the effective power of a lens and indirect measurements of power by translating a lens until collimation is detected.
U.S. Pat. No. 7,688,453 discloses the utilization of a modified Mach-Zehnder (MZ) interferometer to analyze the transmitted, aspherical wavefront of an ophthalmic lens by mounting the lens in a cuvette having a rotatable carousel that can hold multiple lenses. Fresh, temperature controlled saline solution is circulated about the lenses, and the cuvette is positioned in a vertical test arm of the interferometer configuration. Reverse raytracing can be utilized to remove aberrations induced into the measured wavefront as it is imaged by the optical components and lenses in the interferometer system to the detector of the interferometer. If the index of refraction of the contact lens is known, the measured wavefront produced by this measurement can be used to produce a thickness profile of the contact lens.
U.S. Pat. No. 8,641,194 discloses an in vivo method of characterizing dynamic tears using a near infrared phase-shifting interferometer. The interferometer continuously measures light reflected from the tear film, allowing precision analysis of the dynamic surface topography. Movies showing the tear film behavior may be generated along with quantitative metrics describing the tear film surface as it changes in time.
Notwithstanding the usefulness of the above-described methods, a need exists for to provide robust, flexible, sustainable, and accurate metrology of contact lens.